Wednesday, 27 October 2010

An Introduction to the Oxford Clay - Part 2

In the first part of this mini-series, we looked at how the Oxford Clay was deposited and took an overview of the general climate, palaeoecology, and fauna of this highly complex ecosystem. Now I am going to look at some of the more important marine reptiles that have been recovered from this very important rock unit.

For more than 100 years now, the brick-making industry has given us a unique insight into the ancient Jurassic seas. The mud and sediment that accumulated on the sea floor formed the Oxford Clay, and this has been extracted from the brick pits on a massive scale which, in turn, has revealed a myriad of saurian remains.

In England, the area in and around Peterborough has proven to be a rich source. Alfred and Charles Leeds were probably the most significant of the early collectors. The Leeds brothers gathered, en masse, an extensive collection in the early 1900’s and these form the backbone of the marine reptile collections at both the British Museum of Natural History and the Hunterian Museum in Glasgow.

John Phillips was another important collector during the 1920’s and some of his finds reside at the Peterborough City Museum & Art Gallery, as do the more recent discoveries made by Alan Dawn during the 80’s and 90’s. Bedford, Aylesbury and St.Ives in Cambridgeshire are all museums that also hold small collections of Oxford Clay vertebrates.

Also worthy of mention are the substantial collections held at the University of Leicester, which was placed in the repository by both David Martill and Roy Clements, and in the National Museum of Ireland (see Araujo et al 2008).


There are several superb specimens of international significance in the Peterborough collection and these are on permanent display at the Priestgate venue. Amongst these is a virtually complete specimen of the marine crocodile Steneosaurus durobrivensis, more correctly termed a thalattosuchian. This was recovered by Phillips in 1923 and is displayed three dimensionally.

Dogsthorpe Quarry was one of the better known Oxford Clay quarries and during its time was extremely prolific. A more or less complete specimen of Cryptoclidus eurymerus was extracted from Dogsthorpe back in 1984 by Alan Dawn and a group of volunteers from the museum. The skull of this specimen is regarded at the best preserved and most complete ever found.


Even when Dogsthorpe was finished as a clay producing quarry and was being turned into a waste landfill site, it still produced the odd surprise. An employee of Shanks and McEwan, the company who managed the site at the time, discovered the magnificent pliosaur that is Simolestes vorax. This too was excavated by Dawn along with Gordon Chancellor, the then curator at Peterborough Museum. This specimen was virtually complete and well preserved, especially the unique skull which eventually featured as one of the subjects in Dr Leslie Noe’s Phd thesis on Callovian plesiosaurs (2001).

King’s Dyke was another well known and productive quarry. In 1994, yet another new genus of pliosaur was discovered, once more by Alan Dawn. Again largely complete, the skull and cervical vertebrae were almost perfectly articulated and undisturbed, although the rest of the post crania was not. This was the holtype of Pachycostasaurus dawnii and provided yet more new data on plesiosaurian evolution.

Another quarry in the vicinity was Star Quarry, one that I have visited on one occasion and was only flooded last year and is now inaccessible. In 1996 this quarry produced a magnificent, virtually complete specimen of Opthalmosaurus icenicus. This was unusual in as much as the ichthyosaur was recovered from the Middle Oxford Clay (Stewartby Member), much like a previous specimen from King’s Dyke, although this was a far superior example. Originally found by an amateur collector, Nigel Truss, this specimen is also on display in the Peterborough Museum.

Star Pit became the subject of nationwide interest during 2001 when students from Portsmouth University found the remains of the giant fish Leedsichthys problematicus. Estimated at the time to be almost 100 feet long, it is now generally believed to a more conservative, although still massive, 30 feet long.

Once funding had been obtained, Dave Martill, Leslie Noe, Jeff Liston, Darren Naish and students, along with local volunteers from a local geological society began the excavation. Some of this was broadcast nationwide on Channel 4 via their mini-series The Big Monster Dig during 2003.

So it can be seen that not only have these clay quarries had an extremely important social and economic influence in the local area but also gave us a window through time, back to the primordial Jurassic seas. Most exciting of all, as can be seen by the discovery of Pachycostasaurus, there is still so much we don’t know and still discoveries to be made.


There may not be the amount of quarries remaining now but the odd few that remain will continue to produce and it is important that any new discoveries of scientific importance are protected and deposited into the correct repository for both study and for future generations.

Referances

A.R.I. Cruickshank, D.M. Martill and L.F. Noè A pliosaur (Reptilia, Sauropterygia) exhibiting pachyostosis from the Middle Jurassic of England
Journal of the Geological Society.1996; 153: 873-879

Andrews CW. 1913. A descriptive catalogue of the marine reptiles of the Oxford Clay, Part Two. London: British Museum (Natural History) 206pp.

Araujo, R; Smith, A.S. and Liston, J. 2008. The Alfred Leeds fossil vertebrate collection of the National Museum of Ireland - Natural History. Irish Journal of Earth Science, 26, 17-32.

Dawn, A. 1997. Fossil marine reptiles of the Peterborough brick pits. Mercian Geologist, 14, (2), 90-93.

Geoffroy Saint-Hilaire, É. 1825 Recherches sur l’organisation des Gavials, sur leurs affinités naturelles desquelles résulte la nécessité d’une autre distribution générique. Gavialis, Teleosaurus, Steneosaurus. Mémoires du Muséum Histoire
Naturelle 12, 97–155.

Liston, J. 2004. An overview of the pachycormiform Leedsichthys. In Arratia, G. & Tintori, A. (eds) Mesozoic Fishes 3 - Systematics, Paleoenvironments and Biodiversity. Verlag Dr. Friedrich Pfeil (München), pp. 379-390.

Lydekker, R. (1889) Catalogue of the Fossil Reptilia and Amphibia in the British Museum, Part II; Containing the Orders Ichthyopterygia and Sauropterygia. British Museum (Natural History), London, 307 pp.

Martill, D. M. (10) Marine Reptiles. In Martill, D. M. & Hudson, J. D. (eds) Fossils of the Oxford Clay. The Palaeontological Association (London), pp. 226-243.

Noè, L.F. A taxanomic and functional study of the Callovian (Middle Jurassic) Plesiosauroidea (Reptilia, Sauropterygia). Ph.D thesis, University of Derby, Derby. UK

Phillips, J. 1871 The geology of Oxford and the valley of the Thames. Oxford. Clarendon Press.

Seeley, H.G. 1874b On the pectoral arch and forelimb of Ophthalmosaurus, a new ichthyosaurian genus from the Oxford Clay. Quarterly Journal of the Geological Society of London 30,696–707.


Image shows a recently recovered Leedsichthys rib from Quarry 4.

1 comments:

scott davidson said...
This comment has been removed by a blog administrator.

Post a Comment